The document discusses color vision theory and describes: - The primary, secondary, and tertiary colors - How light is detected by the retina and processed by the visual system - Thomas Young and Hermann von Helmholtz's trichromatic theory that the eye contains three types of cone cells sensitive to different wavelengths corresponding to red, green, and blue light - Karl Hering's opponent process theory that the retina contains cells that respond in opposition to colors like red/green and yellow/blue - Different theories on color vision from Aristotle and the role of elements to the modern understanding of cone cell function in the retina.

2. Color Vision Theory

3. Learning Objectives
Point out primary, secondary and tertiary colors
Describe the anatomy of color identification
Narrate the theories of color vision
At the end of the session the trainee will be able to:

4. Colors
It is the light with different frequency that human beings
can see.
Tell the
colors

5. Retina – Visual Impulses
• Chemical Reactions with Photo pigments:
– Cones: “iodopsin” - activated in photopic or bright conditions
– Rods: “rhodopsin” - activated in scotopic or dark conditions
• This begins the visual process
Visual Pigment convert Light Energy into Electrical Energy!

6. Retina – Visual Impulses
Rods and
cones
Bipolar
cells
Ganglion
cells
Optic
Nerve
Brain

7. Activity

8. Color and Light frequency
High frequency
wave length is
Blue / Violet.
Low frequency is
Red
In between
frequency is
green,
yellow,orange,
etc.
Radio Micro
wave
Infrared Visible Ultra
violet
X-Ray Gamma
Ray

9. Colors – Primary, Secondary and
Tertiary
Primary colors : If you mix red, green,
and blue light, you get white light.
Secondary Colors : The colors that are
created from equal amounts of two
primary colors: Purple, orange, and
green
Tertiary colors / Complementary colors :
A pair of colors that are opposite to each
other on the color wheel: Blue and
orange, red and green, yellow and purple.

10. Aristotle’s Theory of Perception
• God sent down color from the
heavens as celestial rays
• He identified four colors
corresponding to the four
elements: earth, Fire, Wind and
water.
• Color vision derives from the
intermingling of elements of light
and darkness.

11. Thomas Young’s – Helmholtz
Trichromatic Theory
Thomas Young in 1802 stated the
existence of three types of
photoreceptors (now known as cone
cells) in the eye, each of which was
sensitive to a particular range of visible
light.
Hermann von Helmholtz in 1850: that the three
types of cone photoreceptors could be classified
as Short wavelength (Blue),
Medium wavelength (Green), and Long
wavelength (Red), as per their response to the
wavelengths of light striking the Retina.

12. Color Vision Concept - Video
Color Vision Concept

13. Color Vision - Afterimages
Afterimages – It is an impression of a bright image retained by
the eye after the stimulus / color has stopped.

14. Opponent process Colour Cell
Theory -Hering’s Theory
Karl Ewald Konstantin Hering in 1892
Three photo chemical substances
in the retina can be broken down
by white, red or yellow light and
will then initiate sensation of
appropriate colors

15. Opponent Color Cell Theory
Cones generate signals of opposite kind depending upon the
light wave-length.

16. Medical meaning
• Protanope – Protan meaning Red sensation missing
• Deutranope – deutan meaning second green
sensation missing
• Tritanope – Tritan meaning blue sensation missing
• Achromatic – free of color / white color